How to Kill Grubs on Roses

Rose bushes (Rosa) are well-known garden plants with more than 150 species. Depending on the species, they grow throughout U.S. Department of Agriculture plant hardiness zones 2 through 11. Roses are not strangers to insects, however, and are susceptible to various pests, including grubs. "Grub" is a general term for the larval stage of beetles, butterflies and moths. Depending on the insect species, the wormlike grubs feed on above-ground and below-ground portions of rose bushes. Fortunately, organic and chemical controls can help to kill grubs and to prevent other grubs from affecting rose bushes.

Organic Control

1

Pick caterpillars and adult beetles off rose bushes while you wear garden gloves. Place the caterpillars and beetles in a bucket of water that is soapy with liquid dish soap.

2

Dilute Bacillus thuringiensis (Bt) with water in a clean garden sprayer. Use the ratio of water to insecticide that is stated on the Bt's label. Bt is a biological insecticide that targets only the larval stage of various insects such as leafrollers, leafhoppers and caterpillars, and it has a low toxicity level to humans, mammals and beneficial insects.

3

Spray each rose bush with the insecticide when no rain is forecast for the 24 hours after you will finish applying the insecticide. Apply the insecticide late in the afternoon if the day is hot and sunny.

4

Repeat the insecticide treatment at 10-day intervals when no rain is forecast for 24 hours after the application.

Chemical Control

1

Remove adult beetles and caterpillars from the rose bushes regularly by hand while wearing garden gloves. Destroy the beetles and caterpillars immediately by placing them in a bucket of water that is soapy with liquid dish soap.

2

Spray the rose bushes when honeybees are not present, using an insecticide containing malathion, carbaryl or pyrethroid cyfluthrin. Insecticide treatment generally is not recommended, however, because it kills only beetles present when the insecticide is applied and because it is harmful to beneficial insects.

3

Repeat the insecticide treatment at seven- to 14-day intervals as stated on the insecticide's label.

Things You Will Need

Garden gloves

Bucket

Liquid dish soap

Bacillus thuringiensis (Bt)

Garden sprayer

Insecticide containing malathion, carbaryl or pyrethroid cyfluthrin

Tip

Consider planting dark-blooming rose bushes in areas where hoplia beetles are a problem. Hoplia beetles feed on the blooms of light-colored rose flowers and tend to stay away from darker blooms.

Each insecticide has specific directions recommended by its manufacturer. Follow the manufacturer's recommended application rate, which is on the insecticide's label, to increase the product's effectiveness and to prevent unintended damage.

Bacterial milky disease and entomopathogenic nematodes have shown some control of grubs when applied to soil. More experiments are needed, however, to determine the actual effectiveness of those control methods.

About the Author

Marylee Gowans has written about gardening for both online and print publications. She attended the University of Akron, graduating with a Master of Fine Arts in creative writing. In 2009, she received master gardener certification from the Master Gardeners of Summit County, Ohio.

Photo Credits

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